Commercial aircraft interiors are generally composed of composite panels decorated with plastic decorative laminates. Preferred decorative laminates have exterior surfaces that are textured and exhibit surface relief. Decorated interior panels are typically formed by heating and then stretching a plastic decorative laminate onto the panel. While textured panels generally retain their surface relief when formed onto smooth and relatively simple contoured panels, significant loss of texture occurs for conventional plastic laminates when they are formed onto compound contoured panels, or when they are formed at higher temperatures and/or under vacuum.
Textured decorative laminates generally include at least two layers; a first embossed layer that imparts surface relief to the laminate and a second decorative layer that overlies the first. The decorative layer is typically either screen printed (i.e., multigraphics) or integrally colored (i.e., internally pigmented).
A laminate construction having a first embossed layer and a second decorative layer is commonly referred to as a single decorative laminate. Generally, the single laminate includes a textured layer consisting of a thermosetting emboss resin (e.g., a 3 mil thick layer of a polyurethane-phenoxy emboss resin) overlaid with a decorative layer composed of a thin layer of pigmented thermoplastic film (e.g., a polyvinyl fluoride film, such as Tedlar.RTM., having a thickness of about 2 mil). A second decorative laminate, commonly referred to as a double decorative laminate, is a laminate construction that includes, in addition to an embossed layer and a decorative layer, a structural layer (e.g., a thermoplastic resinous layer). A typical double decorative laminate includes two thermoplastic layers, an outer decorative layer and an inner structural layer, with an emboss resin layer positioned in between. These decorative laminates are generally prepared by collating sheets of the component plastic materials followed by simultaneously laminating and embossing in a hot press process.
Surface relief or texture is ordinarily imparted to the laminate by a hot press process. During the press cycle, the laminate's thermosetting emboss resin is "molded" by the texture media (i.e., the textured press). The emboss resin is said to be molded because shear flow occurs within the thermosetting resinous material resulting in the layer's cross-sectional thickness variation, i.e., the creation of an embossed or textured surface. The hot press also "forms" the decorative layer. The decorative thermoplastic layer or film is said to be formed because its viscosity is too high for shear flow to occur, and thus cannot be molded and, although the film does stretch during forming onto the textured layer, the decorative film remains relatively uniform in thickness. Furthermore, the heat and length of the hot press cycle result in emboss resin curing or crosslinking, which effectively raises the emboss layer's viscosity and counteracts the residual stresses of the thermoplastic film layer during forming. The crosslinked emboss resin provides for texture retention in subsequent application processes in which the decorative laminate is heated and vacuum formed onto composite panels. However, in some instances, texture inversion can occur as a result of the relatively greater elastic modulus of the decorative thermoplastic layer compared to the textured thermosetting emboss layer.
The conventional thermoset resin-containing decorative laminate constructions described above suffer from several disadvantages including loss of texture retention when the laminate in heated and formed onto a composite panel. For example, single decorative laminates perform poorly when they are elongated more than about 5%, and double decorative laminates begin to lose texture at about 10% elongation. Furthermore, because of the presence of the thermosetting emboss resin, these decorative laminates can only be practically produced in press processes, which are economically disadvantageous for the production of large quantities of laminate.
Accordingly, a need exists for economically produced decorative laminates that retain texture or surface relief when the laminate is heated and formed onto a panel that requires substantial forming or stretching.
There also exists the need for decorative laminates that can be produced by methods other than hot press processes. Because the emboss resin is a thermosetting resin, sufficient time (e.g., from 15 to 30 minutes) above a specific cure or thermoset temperature (e.g., 285.degree. F.) is required to soften and "wet out" the thermoplastic's surface with the thermoset resin for bonding; for shear flow and accommodation of the texture media; and to cure (i.e., crosslink) the thermoset resin for texture retention. Single decorative laminates are generally difficult to roll process because of the misbalance of the elastic modulus of the thermosetting emboss resin and the thermoplastic layer.
A need also exists to overcome the disadvantageous surface properties associated with some pigmented thermoplastic decorative layers. For example, the surface of pigmented polyvinyl fluoride, a common decorative layer, is disrupted by pigment particles that protrude from the material's surface. Because these particles are generally inorganic oxides, the particles are harder than most materials, including metals, that contact the surface. Thus, when metal objects (e.g., jewelry, buckles, coins) rub against this surface with sufficient force, metal is ablated and left on the surface as a dark streak. This phenomena is commonly referred to as "coining." These metallic streaks are difficult to clean because the residual metals are typically not affected by cleaners ordinarily used for cleaning plastic surfaces, and therefore must be abraded from the decorative surface. The pigment particles may also absorb or adsorb other chemicals leaving stains that are also difficult to clean. While it may be possible to force the particles back into the polymer matrix during embossing with heat and pressure, the relatively inelastic nature of the polyvinyl fluoride material requires relatively harsh conditions.
The present invention seeks to provide a decorative laminate that overcomes the difficulties noted above, and provides a decorative laminate that is characterized as having high texture retention when stretched or formed on a composite panel, is readily formed by economical processes, and yet is soft enough so as not to suffer from disadvantageous surface properties.